CI: Add macos-26

Author: bonachea

.github/workflows/CI.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ macos-14, macos-15, macos-15-intel, ubuntu-24.04 ]
+        os: [ macos-14, macos-15, macos-15-intel, macos-26, ubuntu-24.04 ]
         compiler: [ gfortran ]
         version: [ 14 ]
         extra_flags: [ -g ]